Charles Spurgeon Commentary Hebrews 2:18

"For in that he himself hath suffered being tempted, he is able to succor them that are tempted." — Hebrews 2:18 (ASV)

And to whom sware he that they should not enter into his rest, but to them that believed not?

Sinning and not believing seem to go together. The 17th verse asks the same question as the 18th, but the answer is different. With them that had sinned says the 17th verse; to them that believed not says the 18th verse. Lack of faith brings lack of holiness, and when we abide in the faith, we abide in obedience.